Process of solvent bonding napped textile fabric



6 c. R. HUMPHREYS 3,236,586

PROCESS OF SOLVENT BONDING NAPPED TEXTILE FABRIC Filed Aug. 31, 1961FIG.

INVENTOR CHARLES RAYMOND HUMPHREYS BY Md, MW

ATTORNEY United States Patent 3,236,586 PROCESS OF SOLVENT BONDINGNAPPED TEXTILE FABRIC Charles Raymond Humphreys, Wilmington, Del.,assiguor to E. I. du Pont de Nemours and Company, Wilmington, Del., acorporation of Delaware Filed Aug. 31, 1961, Ser. No. 135,315 4 Claims.(Cl. 8130.1)

This invention relates to a method of bonding the fibers in textilematerials and, more particularly, to a method of applying a mist toyarns and fabrics.

In United States application Serial No. 845,339, filed October 9, 1959in the name of Joseph A. Genereux, now abandoned, of which applicationSerial No. 135,316, filed Aug. 31, 1961, now abandoned, is acontinuation-inpart, and which, of the latter application, applicationSerial No. 473,895, filed July 8, 1965, is a continuation, a process isdescribed for improving the properties of textile materials by bondingthe surface fibers having one free end. This process is particularlyvaluable, since it reduces the shedding and surface distortion of nappedfabrics without increasing their stiffness. It is of particular value inthe preparation of blanket materials and has been observed to provideimproved resistance to shrinkage. In scale-up operations it has beenfound that application of the process of Genereux, identified above,when the mist is applied to both sides of a fabric simultaneously whileit is traveling in a horizontal position, difficulties in commercialproduction are sometimes encountered.

It is an object of the present invention to provide a novel and usefulimproved means of applying vaporized finish liquids to the surface offabrics.

Another object is to provide apparatus suitable for the application offinishes such as described in the Genereux application without theformation of spots and other surface defects.

These and other objects will become apparent in the course of thefollowing specification and claims.

The above objects are accomplished by providing a process for bondingfibers of a textile material which comprises applying to both sides of atextile material, while the said textile is in a full width conditionand vertically disposed, a mist composed of discrete liquid particles,substantially all of which are less than .012 inch in size, dispersed ina gaseous medium, each liquid particle resulting from the atomization ofa liquid comprising from about 1% to about 25 of a latent solvent forthe fiber in a volatile diluent which is inert to the fibers to bebonded, the quantity of solvent being by weight of the total liquid,under conditions such that no fibers are substantially displaced withinthe textile material and the textile material maintains its originalthickness, then activating the latent fiber solvent to cause bonding ata number of points in the material where two or more fibers contact eachother, and removing the excess diluent, and optionally the solvent.

The invention will be more readily understood by reference to thedrawings. FIGURE 1 is a schematic diagram showing the fiow of the fabricthrough the various steps of the process. In the figure, fabric 1,preferably in a vertical position, held at full width by securing means(not shown) along its edges (preferably by pins), passes into shieldarea 2, wherein a mist 3 is applied to each side of the moving fabricfrom nozzles 4. Thereafter the fabric is led around guide rolls 5 into adrying tenter frame 6 wherein heat is applied to remove the diluent,after which the still tentered fabric is cooled, and then the cooledfabric proceeds to the fabric collector 7, which collects the fabric byconventional means, such as by wind-up, folding, lapping, or the like.

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FIGURE 2 shows the system in greater detail. In this figure fabric 1,preferably on a pin frame, is directed over swivel 8 and thereafteraround guide 9 to place it in a vertical position. Thereafter it entersthe shield area 2, containing the web-wetter 10 which contains nozzles 4(not shown). Shield area 2 is equipped with fume exhaust 11. Whenleaving the shield area the fabric is trained around guides 12, 13 and14 into drying tenter frame 6, then, while still tentered, is cooled andthereafter proceeds to fabric collector 7.

As a typical way of carrying out the invention, a woven blanketconsisting of 100% polyacrylonitrile fibers distributed in the blanketsuch that approximately 25% of the total thickness of the blanket is inthe center and of the total thickness of the blanket is in the nap onboth surfaces of the fabric is treated. A suitable mist for bonding thispolyacrylonitrile blanket was prepared from an aqueous solutioncontaining 5% sodium thiocyanate by weight by misting said solution inthe web-wetter described in the example given hereinafter. The blanketwas fed continuously in a vertical position between two nozzles of theweb-wetter without coming in contact with the apparatus while tinydroplets of the liquid from the mist deposit on both sides of theblanket. The fabric then was led directly through a 15-foot drying ovenmaintained at 300 F. at a speed of two yards per minute in order toactivate the fiber solvent by evaporation of the diluent to bond thefibers at a number of crossover points. The oven also served to removeall of the diluent, leaving a completely dry (i.e., non-tacky) fabric.The dried bonded fabric picked up 0.07 gram of sodium thiocyanate persquare yard of each fabric face. This bonded fabric exhibited lessshedding and less surface distortion than the equivalent unbondedcontrol fabric.

Surprisingly, it has been found that the stiffness of the bonded fabricis directly and primarily dependent upon the quantity of fiber solventpicked up on the face of the fabric, whereas the resistance todistortion and shedding resistance of the fabric are dependent upon boththe quantity of fiber solvent picked up on the fabric face as well asthe concentration of latent fiber solvent in the liquid solution fromwhich the mist is formed. Therefore, in order to achieve bonded fabricswith a desirable combination of stiffness and shedding resistance, atleast two factors involving the fiber solvent are highly critical. Theconcentration of latent fiber solvent in the mist-forming solution mustbe between about 1% and 25% of latent fiber solvent based on the weightof the total solution, and preferably between 4% and 6% when usingsodium thiocyanate as the latent fiber solvent for bondingpolyacrylonitrile fibers. Also, in the case of using sodium thiocyanate,for example, as a latent fiber solvent for polyacrylonitrile fibers, thequantity of thiocyanate salt deposited on the fabric (dry weight) shouldbe between 0.02 and 1.0 gram per square yard of each fabric face, and amore optimum range of fabric stiffness values for blankets is obtainedwhen this quantity is between 0.06 and 0.15 gram.

By latent fiber solvent as used herein is meant any liquid or solidmaterial or solution of same, soluble or miscible in the liquid medium,which is, in the initial single phase liquid solution, a non-solvent forthe fiber but is capable of bonding (i.e., at least rendering the fibersurface tacky) the fiber after activation of the latent solvent. Thefiber solvent may be used herein by dissolving it in a separate liquidsolvent for the same or by using it alone in the liquid mediumspecified.

Typical fiber solvents for acrylonitrile polymer fibers include aqueoussolutions of sodium thiocyanate, lithium thiocyanate, lithium iodide,sodium iodide, calcium thiocyanate, potassium thiocyanate, calciumbromide, zinc chloride, lithium bromide, magnesium thiocyanate, cupricchloride, magnesium chloride, ferric chloride, ferrous bromide, cadmiumiodide, barium chloride, and cobaltou-s iodide. Suitable fiber solventsalso include propylene carbonate, ethylene carbonate, dimethyl sulfone,tetramethylene sulfone, dimethyl forma-m-ide, dimethyl acetam-ide gamm-abutyrolactone, trimethylene carbonate, and the like. These may bedissolved in water, or many of them may be dissolved in alcohol,ethylene glycol, benzene or the like. Typical fiber solvents forpolyamide fibers include aqueous solutions of the inorganic salts listedabove for acrylonitrile polymer fibers, .as well as materials such asnitric acid, formic acid, phenol, metacresol, and the like. These may bedissolved in water, ethanol, methanol, benzene, and the like, dependingupon the fiber solvent used. Typical fiber solvents for polyester fibersinclude benzyl alcohol, benzoic acid, dichloro acetic acid, trichloroacetic acid, trifiuoro acetic acid, dichloro phenol, and aqueoussolutions of calcium and magnesium thiocyanate. Similarly, knownsolvents for other polymers listed below may be used when such polymersare present. In the case of natural fibers, etc., any known solvent maybe used. Typical solvents suitable for wool include alkali metal saltsof thioglycolic acid, and sodium sulfide. Dilute aqueous solutions offerric chloride, etc., are suitable for rayon.

The liquid medium employed in the preparation of the one-phase liquidsolution of this invention may be the same liquid as used for dissolvingthe fiber solvent when desired, as illustrated above in the lists offiber solvents, or the liquid medium may be a different liquid which ismiscible with the liquid employed to dissolve the fiber solvent. Theliquid medium may be aqueous or organic or a mixture of two or moreliquids which are miscible with one another. In each case the liquidmedium should be capable initially of dissolving the fiber solvent toform the single phase liquid solution. The liquid medium should berelatively inert to the fibers of the fabric and should not be a goodsolvent for the polymer from which the fibers are made.

Although the composition of the liquid solution will normally be limitedto consist essentially of two ingredients (i.e., latent fiber solventand liquid medium), it may be advantageous in treating certain textilematerials to employ in the solution small amounts of inert extenders(such as polyethylene oxide), softeners, antistats, slickening agents,sizes and finishes, pigments and dyestuffs, and other adjuvants whichcan be dissolved or dispersed in the solution to achieve particularresults. However, these additional adjuvants must be carefully chosen inamount and composition so as not to disrupt the cooperating function ofthe two main ingredients of the. solution in storming the mist anddirect application and processing of the mist on the textile material.

The textile materials which may be treated in accordance with thisinvention may include sliver, tow, yarns, warps, batts, and woven,knitted, and non-woven fabrics. The woven fabrics may be woolen spun orworsted spun fiannels, tweeds, shetlands, blankets, carpets, pilefabrics and the like. The knitted fabrics may be warp knitted orcircular knitted jersey, sweaters, pile fabrics, socks and hosiery,suitings, gloves, scarfs, and the like. The nonwoven fabrics may becarpets, upholstery, fleeces, furs, fiannels, sweaters, felts, hats, andthe like.

The composition of the staple fibers and/or continuous filaments makingup the textile materials should be at least by weight of organic,polymeric fibrous material capable of being bonded in order to achievebenefit from the misting treating in accordance with this invention.Blends of synthetic and/ or natural fibers may be advantageously treatedwhere all the fibers are to be bonded, or the solutions may be carefullychosen so that they are inert with respect .to the fibers present thatare not to be bonded.

Typical of the synthetic onganic fibers and filaments which may betreated according to this invention include 4 those prepared frompolyamides such as poly(hexamethylene adipamide), poly(hexamethylenesebacamide),

polycaproamide, and copolyamides, polyesters, and copolyesters such ascondensation products of ethylene glycol with terephthalic acid,ethylene glycol with a /10 mixture of terephthalic/is'ophthalic acids,ethylene glycol with a 98/2 mixture of terephthalic/S-(sodiumsulfo)-isophthalic acids, and trans-p-hexahydroxylylene glycol withterephthalic acid, polyacrylonitrile, copolymers of acrylonitrile withother monomers such as vinyl acetate, vinyl chloride, methyl acrylate,vinyl pyridine, sodium styrene sulfonate ter polymers of acrylonitrile/methyl acrylate/sodium styrene sulfionate made in accordance with UnitedStates Patent 2,837,501, vinyl and vinylidene polymer and copolymers,polyesteramides, polyethylenes, polypropylenes, fiuorinated ethylenepolymers and copolymers, cellulose derivaties, such as celluloseacetate, cellulose triacetate, rayon, viscose, etc. composite filamentssuch as, for example, a sheath of polyamides around a core of polyesteras described in the copending application of Breen, United States SerialNo. 621,443, filed November 9, 1956, now abandoned, and of whichapplication Serial No. 771,676, filed November 3, 1958, is acontinuation-in-part and which is now US. Patent No. 3,038,236 and twoacrylonitrile polymers differing in ionizable group content spun as asheath and core as described in the copending application of Taylor,United States Serial No. 640,722, filed February 18, 1957, nowabandoned, and of which application Serial No. 771,677, filed November3, 1958, is a continuationin-part and which is now US. Patent No.3,038,237, and the like. The fibers and filaments may be crimped oruncrimpcd, drawn or undrawn, and/or bulked or unbulked.

Another highly critical factor in the present invention is the particlesize of the discrete liquid particles which form the mist being appliedto the textile materials. The maximum size of these liquid particlescomprising liquid fiber solvent and diluent is about .012 inch. When thesize of these liquid particles in the mist are much above the criticalmaximum given, the bonded resulting fabrics lose their good hand andaesthetics, the [fabrics become undesirably still? and blankets bondedwith too large a particle have an undesirable loss in thickness of nap.Any suitable apparatus or method for forming a fine mist of discreteliquid particles less than .012 inch in size is suitable herein. Thereare commercially available humidifiers, fog nozzles, mist formingapparatus, sprayers, and the like. One particularly suitable form ofapparatus for practicing this invention is one that atomizes the liquidsolution into a mist, such as the humidifiers described in theFelderm-ann Patents; 2,022,415 and 2,591,057. This type of humidifierproduces a mist having a wide distribution of liquid particle sizes. Thelarge heavy particles which are unsuitable for bonding the fibers inaccordance with this invention, strike the walls of the humidifier,coalesce and fall back into the supply tank so that none of these largeliquid particles ever contact I the fibers or the fabric being bonded,only a portion of the smaller particles ever reach the fabric. Thediscrete liquid particles in the mist used in this invention areessentially round.

Another important limitation of the present invention lies in theconditions under which the mist is applied to the textile material. Themist of discrete liquid particles must contact the surface of the yarn,fabric, or other textile material without any accompanying mechanicalcompressive force such as the application of a roller or padder. Inaddition, the particles of the mist must not contact the textilematerial at such high speeds that they compress the fibers in any sense.In this connection, many of the commercial patented sprayers areunsuitable for applying a mist in accordance with this invention becausethe air and/or liquid pressure developed in the nozzle of the sprayer isso strong that it compacts the surface fibers of the textile material,which act reduces the thickness of the pile of napped fabrics andblankets and decreases the other desirable properties of these textilematerials. Also, the use of these high pressures for forcing the liquidparticles against the textile material results in non-uniformapplication of the liquid fiber solvent across the width of the fabricbeing treated which leads to fabrics having non-uniform properties andmakes it difiicult or impossible to reproduce fabrics having the sameproperties.

Normally the mist is applied to the surface of the textile material atroom temperature, although the temperature of the mist or the fabric maybe elevated so long as it is well below the temperature necessary toconvert the latent fiber solvent to an active fiber solvent for thefibers. A suitable temperature range for drying and bondingpolyacrylonitrile fibers is from 215 F. to 350 F., and preferably from250 F. to 300 F. for one to five minutes contact time. Obviously thetemperature of application of the fog, drying and bonding should not beso high that it melts the surface fibers of the textile material ordeforms the surface fibers to such an extent to destroy their fibrouscharacter.

The chief advantage of this invention is the provision of a novelprocess for bonding the fibers of textile materials, and particularly,loose surface fibers. Another advantage is the fact that the processprovides a method for making blankets which have high resistance tosurface distortion and high resistance to shedding without affecting thegood hand of the blanket and without reducing the thickness of the napof the blanket. Another advantage is a process for reducing the sheddingand fuzzing of yarns and fabrics without substantially affecting thestiffness of the yarn or fabric. Still another advantage lies in thefact that the method of the present invention reduces the fuzzing andpickiness of non-woven fabrics. Another advantage is that this processproduces blankets having improved resistance to surface distortion uponrepeated washings and launderings. The process of this invention alsoproduces bonded fabrics which have greater cover and smoothness than theunbonded fabrics.

The following example is cited to illustrate the invention and is notintended to limit it in any manner.

EXAMPLE Using the arrangement shown in FIGURE 2, a woven napped blanketmade from staple fibers of a copolymer of 94% acrylonitrile and 6% ofmethyl acrylate is passed vertically upwards between two nozzles whichpropel a fine mist against both surfaces of the fabric simultaneously,said mist being propelled at an oblique angle in the direction of fabrictravel, while the fabric is tentered. The mist is generated in aWeb-Wetter, which is available from Walton Laboratories, Inc.,Irvington, New Jersey. The Web-Wetter is continuously charged through afeed line from a reservoir with an aqueous solution containing 5% sodiumthiocyanate by weight. The speed of the fabric as it is passed throughthe mist is approximately 10.5 yds./min. After passing through the mist,the still tentered fabric is fed through a drying oven containingcirculating air at 300 F. The length of the drying oven is 55 feet. Thetentered fabric then passes immediately through a 35 foot length coolingchamber containing still air at room temperature. Special precautionsare taken during the fabric treatment with mist so as to avoidcompacting either surface of the fabric. The resulting fabric is foundto have an excellent hand, and to be very uniform and smooth inappearance. The fabric undergoes no substantial change in hand orappearance even after three washings in a home washing machine. Beforewashing, the dry fabric was analyzed and found to contain 0.13 gram ofsodium thiocyanate per square yard of each fabric face. No spotting isnoted, which is characteristic of fabric when treated with the same mistfrom both sides simultaneously, while the fabric passes horizontallybetween two misting nozzles. As the concentration of sodium thiocyanateis increased above 5%, there is no appreciable effect upon theappearance of the fabric, but its stiffness increases.

While the invention has been illustrated by treatment of a nappedpolyacrylonitrile blanket, it is to be understood that the identicalsteps may be used to apply a mist containing known solvent to textilematerials made from any other polymer which is amenable to bonding bythe application of a liquid which has substantially no solvent effect onthe polymer at room temperature but which may be activated by heating torender the polymeric fibers cementitious at contact points where adroplet of the mist has been deposited, and the solvent may subsequentlybe removed, leaving the fibers point bonded. As shown in the drawingsthe fabric may be treated with mist while moving vertically downwards orupwards or it may move along its edge while vertically disposed.

The foregoing detailed description has been given for clearness ofunderstanding only and no unnecessary limitations are to be understoodtherefrom. The invention is not limited to the exact details shown anddescribed for obvious modifications will occur to those skilled in theart.

What is claimed is:

1. In a process for bonding contiguous fibers of a napped fibroustextile fabric having substantial thickness in which the surface fibershave one end held within the fabric structure and one free end raisedtherefrom forming a nap thereon wherein a controlled amount of a liquidcontaining 1 to 25 weight percent of a latent solvating material forsaid fibers is deposited simultaneously on both surface of said textilefabric in the absence of substantial propelling force and in the form ofa mist of discrete liquid particles having an average particle size ofless than about 0.012 inch in diameter with said fibers being maintainedin their relative positions without significant displacement whiledepositing said particles thereon and contiguous fibers are bondedwithout compression of the nap at points where said particles have beendeposited solely by employing said discrete liquid particles and byheating the treated fabric to a temperature in the range of 215 F. to350 F. to activate the solvating material, the improvement whichcomprises directing said textile fabric in a vertical path whiledepositing said liquid particles on said fabric.

2. The process of claim 1 wherein the fibers to be bonded are made ofacrylonitrile polymer.

3. The process of claim 2 in which the liquid from which said mist isformed contains from about 4% to 6% of sodium thiocyanate in aqueoussolution.

4. The process of claim 2 in which the liquid from which said mist isformed is aqueous ethylene carbonate.

References Cited by the Examiner UNITED STATES PATENTS 738,347 9/ 1903Myers. 1,547,513 7/1925 Morden 8l49.2 1,796,039 3/1931 Mijer 8149.21,978,034 10/1934 Sutherland 117-106 2,390,386 12/1945 Radford.2,869,975 1/ 1959 Hare. 2,920,992 1/1960 Hubbard 117--140 X 3,053,6099/1962 Miller.

J. TRAVIS BROWN, Acting Primary Examiner.

JOSEPH B. SPENCER, NORMAN G. TORCHIN,

Examiners.

T. G. DAVIS, H. WOLMAN, Assistant Examiners.

1. IN A PROCESS FOR BONDING CONTIGUOUS FIBERS OF A NAPPED FIBROUSTEXTILE FABRIC HAVING SUBSTANTIAL THICKNESS IN WHICH THE SURFACE FIBERSHAVE ONE END HELD WITHIN THE FABRIC STRUCTURE AND ONE FREE END RAISEDTHEREFROM FORMING A NAP THEREON WHEREIN A CONTROLLED AMOUNT OF A LIQUIDCONTAINING 1 TO 25 WEIGHT PERCENT OF A LATENT SOLVATING MATERIAL FORSAID FIBERS IS DEPOSITED SIMULTANEOUSLY ON BOTH SURFACE OF SAID TEXTILEFABRIC IN THE ABSENCE OF SUBSTANTIAL PROPELLING FORCE AND IN THE FORM OFA MIST OF DISCRETE LIQUID PARTICLES HAVING AN AVERAGE PARTICLE SIZE OFLESS THAN ABOUT 0.012 INCH IN DIAMETER WITH SAID FIBERS BEING MAINTAINEDIN THEIR RELATIVE POSITIONS WITHOUT SIGNIFICANT DISPLACEMENT WHILEDEPOSITING SAID PARTICLES THEREON AND CONTIGUOUS FIBERS ARE BONDEDWITHOUT COMPRESSION OF THE NAP AT POINTS WHERE SAID PARTICLE HAVE BEENDEPOSITED SOLELY BY EMPLOYING SAID DISCRETE LIQUID PARTICLES AND BYHEATING THE TREATED FABRIC TO A TEMPERATURE IN THE RANGE OF 215*F. TO350*F. TO ACTIVATE THE SOLVATING MATERIAL, THE IMPROVEMENT WHICHCOMPRISES DIRECTING SAID TEXTILE FABRIC IN A VERTICLE PATH WHILEDEPOSITING SAID LIQUID PARTICLES ON SAID FABRIC.
 2. THE PROCESS OF CLAIM1 WHEREIN THE FIBERS TO BE BONDED ARE MADE OF ACRYLONITRILE POLYMER.